Surface treated plastic materials and method for producing same



United States Patent SURFACE TREATED PLASTIC MATERIALS AND METHOD FOR PRODUCING SAME Luther L. Yaeger, Madison, Wis., assignor to American Motors Corporation, a corporation of Maryland No Drawing. Original application January 28, 1948, Serial No. 4,945. Divided and this application April 14, 1951, Serial No. 221,117

8 Claims. (Cl. 117-103) This invention relates to the improvement of plastic articles and particularly to treatments for the improvement of surface properties of polystyrene.

The present application is a continuation in part of the co-pending application Serial No. 730,192 filed February 21,1947, and now Patent No. 2,578,665 and is a divisional application of Serial No. 4,945, filed January 28, 1948 and now Patent No. 2,652,339.

Heretofore the practical use of polystyrene resins has been hampered by the following undesirable surface characteristics: sensitivity to crazing, sensitivity to common organic solvents, and extreme electrostatic attraction for dust. These disadvantages were overcome by the development of the integrally bondable coatings for styrene, which were disclosed in the above-mentioned patent application, of which this application is a continuation in part.

An object of the present application is to provide improved coating compositions, for polystyrene. Another object is a composition having increased solvent resistance, and being integrally bendable to polystyrene. A still further object is a coating having a higher margin of safety with regard to attack on polystyrene, than has previously been possible.

Further objects will become apparent, as the description proceeds.

In accordance with this invention, I employ as component solvents in the coating compositions, nitromethane, or other mononitrated hydrocarbons having less than four carbon atoms, or mixtures thereof. This makespossible the formulation of coating compositions having the just mentioned distinct advantages.

In the co-pending application already mentioned, the solvents disclosed permitted use as a film former only of cellulose acetobutyrates in which the acetyl content was less than about 8%, and the butyryl content was about 45-50%. If the high solvency ingredients such as the ketones or the aromatic solvents were increased materially, then the styrene would be attacked even before the required solvency was reached for the more resistant high acetyl types of cellulose aceto butyrate.

I have found that the use of nitromethane, or certain other mononitro derivatives further to be detailed below, in conjunction with preponderantly alcohol-type solvents, makes possible the use of the high resistance type cellulose mixed esters, without damage to the polystyrene. The invention is illustrated by the following specific examples, which are given by way of illustrations and not in any sense of limitation. The parts given in the examples are 2,702,255 Patented Feb. 15, 1955 ICC While this is a preferred formula, it can be simplified considerably. while retaining adequate performance. For example, the methyl ethyl ketone and the ethyl lactate may beomitted, and the glycolether can be limited to a single member of the series.

Example 3 Ethylene glycol monoethyl acetate 5.2 Nitromethane 94 Cellulose acetobutyrate, containing 20% butyryl and 40% acetyl groups The composition resulting upon mixing the three above ingredients was applied to polystyrene by spraying. It formed an integrally bonded coating, resistant to the infiuence of the common solvents and to marring. When the nitromethane content is very high, say above about 80%, it is desirable to have present at least about 5% of an ester or ketone type solvent.

Example 4 Cellulose ester, having an acetyl content of 35%, a butyryl content of 15% and a propionyl content of 15% Ethyleneglycol monomethyl ether 49 Diacetone alc h l 30 Nitromethane l0 Ethyleneglycol monoethylether acetate 10 This coating bonded integrally with good clarity, upon dipping a polystyrene panel into the composition, and allowing to dry at room temperature for 24 hours.

Example 5 Cellulose ester, having an acetyl content of 43% and a propionyl content of 16% Polyethyl acrylate- 1 Polyethyl methacrylate 3 Ethyleneglycol monoethyl ether acetate 10 Ethyleneglycol monomethyl ether 50 Diacetone alcohol 30 Nitromethane 30 Nitropropane 10 Nitrobutane 2 by weight.

Example 1 Ethyleneglycol mono ethyl ether acetate 6 Methyl ethyl ketone ll Ethylene glycol monoethyl ether 77 Ethyl lactate 6 Nitromethane 27 Cellulose acetobutyrate having acetyl content of 40% and butyryl content of 20% 7 A polystyrene panel was dipped into this composition, and was then dried under infra red lamps at F. In twenty minutes a firm protective coating A part of the methacrylate polymer remained undissolved, and was removed by centrifugation. A polystyrene panel was dipped into the resultant product, and dried as in the preceding example. A clear, integrally bonded protective coat resulted.

Example 7 An acrylate polymer was prepared in the following manner:

Methyl methacrylate monomer 21 n-Butyl methacrylate monomer 6 2,4-dichlorobenzoyl peroxide.. 1

The acrylic polymer prepared as just stated l Cellulose aceto butyrate with acetyl content 37%, butyryl content 19% Nitroethane 20 Ethanol anhydrous 5 Ethyleneglycol monomethyl ether 30 Diacetone alcohol 20 The product thus obtained was sprayed onto polystyrene articles, and, on drying, formed an integrally bonded resistant coating.

While reference has been made to certain specific embodiments of the invention, it should be fully understood, that these are by way of example only, and are not to be construed in any sense of limitation.

The nitro derivatives in question may be used in percentages from about 5 up to 95% for nitromethane, and from 5 up to 90% of nitro derivatives having less than 4 carbon atoms, to increase the solubility of other high resistance cellulose esters in alcohol type solvents, which, without the nitrohydrocarbons, would not be capable of dissolving these solvent cellulose esters; or, if compounded with ketones or aromatic hydrocarbons to give the necessary solvency, would attack polystyrene so as to be unsuitable for use with polystyrene, as contemplated in this application. The alcohol type solvents disclosed have a boiling range between about 140 and 350 F., and include glycols and glycol mono esters and ethers, ethanol, methanol, propanol, butanol, the isomers of amyl alcohol, and generally hydroxyl containing solvents having the same general solvent characteristics as these compounds, with reference to the cellulose ester and to polystyrenes.

The high resistance cellulose esters referred to in this application are characterized, for example, by being insoluble and substantially non-softening in toluol and in ethyl alcohol. These esters have an acetyl content of at least 8%, and the remaining esterifying radicals are preponderantly of acid groups having from 2 to 4 carbon atoms. It might be possible to use a small percentage of higher molecular acids in the esterification of the cellulose, but this is not preferred for the purpose of this invention.

The expression integrally bonded as used herein, is intended to convey that the coating to all practical intents and purposes forms one body with the underlying polystyrene; it cannot be removed from it by any amount of mechanical persuasion and it is not possible to discern by the naked eye at which point one layer begins and the otherends.

The expression polystyrenes is understood to include also co-polymers or mixtures, in which polymers of monostyrene are the dominating and preponderant ingredient.

In applying the treatment of this invention, it is preferable that the relative humidity should be below 60%. If the humidity is higher than this, the coating is apt to cloud, unless the evaporation is carried out with extreme caution and very slowly. This clouding, however, is avoided by warming the treated surface with infra-red lamps or by pre-heating the air current to temperatures between 110 and 170 F. Under these conditions the coating composition of Example 1, for instance, will dry in about 10 minutes to a point where the articles can be handled and in 20 minutes it will be completely dry. The coating will attain its true hardness in 24 hours on standing.

The present invention makes it possible, likewise, to apply a hlghly resistant surface coating to extremely thin fibers made by extruding and/or drawing polystyrene type resins. For example, fibers made by extruding polystyrene were passed through the solution of Example 1 in which the solid content had been reduced to a third, while maintaining the proportions otherwise unchanged. The fibers were dried in an air current of F., and were found to be resistant to dry-cleaning solvents. The various conditions of application mentioned above apply to polystyrene type resin surfaces, regardless of the nature of these surfaces, and thus also include the field of fibers.

The ester and ketone type solvents used are employed in percentages from 0 to about 25%. Any esters and ketones boiling between 130 and 350 F. can be employed. For example useful substances in this group are acetone, methyl ethyl ketone, dibutyl ketone, ethyl afietlage, butyl acetate, amyl acetate, methyl butyrate and The nitro derivatives contemplated include all of the mononitrated aliphatic hydrocarbons, which contain less than four carbon atoms.

The cellulose esters include mixed cellulose esters with aliphatic groups containing from two to four carbon atoms. The preferred cellulose esters for the purposes of this invention are those which have the 2-carbon groups in a preponderance, because the acetic and oxyacetic esters appear to impart to the films an exceptional surface resistance. Such esters with 8 to 50% of acetyl groups are usable for the invention, but the range of 8 to 40% of acetyl groups is preferable. On the other hand, the nitroparafiinic solvent combinations here described can also be employed for products containing cellulose esters in which propionyl, oxy propionyl, halopropionyl or corresponding butyryl derivatives predominate, though these are not generally as resistant as the preferred coatings disclosed herein.

As shown in the examples, I may find it expedient or desirable to include in the solvent composition minor percentages of still other solvents. The claims are not to be circumvented by the inclusion of such minor percentages of ancillary or auxiliary solvents.

I often prefer to include in the solid part of the nonvolatile part of the composition an acrylate, methacrylate, chloroacrylate or crotonate resin. This, also, is not an indispensable part of the invention, as these resins can be dispensed with. I may include still further resinous or other materials, such as, for example, cellulose oxyacetate, non-drying plasticizing alkyds, phenyl salicylate, phosphor and other pigments, including phthalocyanines, and spirit soluble dyes. The inclusionof minor percentages of these or other additional ingredients is not to be construed as a means of circumventing the claims, as these and similar additions are permissible, but irrelevant to the invention, the salient features of which are embodied in the claims. It is thus seen that the invention is broad in scope, and is not to be limited excepting by the claims. in which it is my intention to cover all novelty inherent in the invention as broadly as possible, in view of prior art.

Having thus disclosed my invention I claim:

1. The process of imparting solvent resistance to poly-.

styrene, which comprises the step of applying to said polystyrene a composition of sprayable consistency, comprising a mixed cellulose ester in which the esterifying groups are preponderantly radicals containing two carbon atoms, and none of which has more than four carbon atoms, and which has an acetyl content of at least 8%; dissolved in a solvent containing 5 to 35% of a nitro-alkane containing one to 3 carbon atoms, the remainder of the solvent consisting essentially of aliphatic alcohols having a boiling range between about and 350; and removing said solvents at a relative humidity less than 60%.

2. The process of imparting solvent resistance to polystyrene, which comprises the step of applying to said polystyrene a composition of sprayable consistency, comprising a mixed cellulose ester in which the esterifying groups are preponderantly radicals containing two carbon atoms, and none of which has more than four carbon atoms, and which has an acetyl content of at least,

face a solution consisting essentially of a resin selected from a group consisting of acrylate and methacrylate polymers, and a mixed cellulose ester in which the esterifying groups are preponderantly radicals containing from two to four carbon atoms and having an acetyl content of at least 8%; the said resins being dissolved in a solvent containing from to 35 of a nitro-alkane containing 1 to three carbon atoms, the remainder of the solvent consisting essentially of aliphatic alcohols having a boiling range between about 140 and 350 F., and renoving said solvents at a relative humidity less than 60 0.

4. The process of imparting solvent resistance to polystyrene, which comprises the step of applying to said polystyrene a composition of sprayable consistency, comprising a mixed cellulose ester in which the esterifying groups are preponderantly radicals containing two carbon atoms, and none of which has more than four carbon atoms, and which has an acetyl content of at least 8%; dissolved in a solvent containing 5 to 35% of a nitroalkane containing from one to 3 carbon atoms, and removing said solvents at a relative humidity less than 60%.

5. The process of imparting solvent resistance to polystyrene, which comprises the step of applying to said polystyrene a composition of sprayable consistency, comprising a mixed cellulose ester in which the esterifying groups are radicals containing 2 to 4 carbon atoms and which has an acetyl content of at least 8%; dissolved in a solvent containing 5 to of a nitroalkane containing one to three carbon atoms, and removing said solvents at a relative humidity less than 6. As an article of manufacture, a textile fiber comprising a core comprising polystyrene, and surrounding this, a sheet of a plastic consisting essentially of cellulose acetate butyrate having an acetyl content of 8% to 43% and a butyral content of 15% to 22%.

7. An article of manufacture comprising polystyrene having integrally bonded thereto a layer consisting essentially of a mixed cellulose ester in which at least one of the esterifying groups is an acid having from 2 to 4 carbon atoms and which contains 8% to 43% acetyl radical.

8. An article of manufacture comprising a polystyrene surface having a layer integrally bonded thereto consisting essentially of a mixed cellulose ester in which at least one of the esterifying groups is of an acid having 2 to 4 carbon atoms, the said cellulose ester containing 8% to 43% acetyl groups.

References Cited in the file of this patent UNITED STATES PATENTS 2,229,617 Wampner Ian. 21, 1941 2,332,461 Muskat et a1. Oct. 19, 1943 2,393,863 Myers Jan. 29, 1946 2,578,770 Yeager Dec. 18, 1951 

1. THE PROCESS OF IMPARTING SOLVENT RESISTANCE TO POLYSTYRENE, WHICH COMPRISES THE STEP OF APPLYING TO SAID POLYSTYRENE A COMPOSITION OF SPRAYABLE CONSISTENCY, COMPRISING A MIXED CELLULOSE ESTER IN WHICH THE ESTERIFYING GROUPS ARE PREPONDERANTLY RADICALS CONTAINING TWO CARBON ATOMS, AND NONE OF WHICH HAS MORE THAN FOUR CARBON ATOMS, AND WHICH HAS AN ACETYL CONTENT OF AT LEAST 8%; DISSOLVED IN A SOLVENT CONTAINING 5 TO 35% OF A NITRO-ALKANE CONTAINING ONE TO 3 CARBON ATOMS, THE REMAINDER OF THE SOLVENT CONSISTING ESSENTIALLY OF ALIPHATIC ALCOHOLS HAVING A BOILING RANGE BETWEEN ABOUT 140* AND 350*; AND REMOVING SAID SOLVENTS AT A RELATIVE HUMIDITY LESS THAN 60%. 